Friday, May 09, 2008

Female seagulls come out on top

Talk about a sibling rivalry. Some birds are so eager to better their brothers and sisters that they eavesdrop on unhatched eggs.

It turns out many birds start squawking days before they bust loose, and siblings listen to each other to time their hatches. Few birds want to be the last chick out of the egg - often the runt of the litter and neglected by its parents. But sometimes waiting pays off: more time in the shell means bigger muscles, potentially upping a bird's chances of besting an older sibling.

Rivalries between brothers and sisters can be especially intense, and now a team of Scottish researchers studying seagulls has come to a surprising conclusion about who comes out on top - though not necessarily first.

Maria Bogdanova and Ruedi Nager of the University of Glasgow reared male and female seagull eggs in isolation or in contact with the eggs of their two siblings (seagulls usually lay three eggs at a time). When the gulls broke free, the researchers compared males and females raised as only children or in a family.

Brothers reared alone tended to hatch earlier than sisters. In a family nest that difference disappeared, presumably because the brothers waited to spring loose. And no matter their sex, the babies reared alone did best - they left their nest, or fledged, in good shape. Not so for the brothers hatched and raised among sisters. They fledged smaller and in worse shape than their siblings.

What to make of this? Bogdanova and Nager think that baby brothers, because they demand extra food and attention, might end up neglected by their parents no matter when they hatch. So much for the "weaker sex".